Apparatus for making rubber covered carbon black pellets

ABSTRACT

Carbon black pellets are covered with rubber to prevent dusting problems. In a process and apparatus for covering carbon black pellets with rubber the carbon black pellets are introduced into a coating chamber comprising a porous cylinder into which fluid rubber containing material is injected, which material is picked up by the individual carbon black pellets while they are coated by this material.

This is a division of application Ser. No. 367,857, filed Apr. 13, 1982, now U.S. Pat. No. 4,440,807, which is a division of application Ser. No. 145,908, filed May 2, 1980, now U.S. Pat. No. 4,337,294.

The present invention relates to the production of dust free carbon black pellets. More specifically the present invention relates to the production of carbon black pellets having a cover which prevents the development of carbon black dust during the transportation and use of these carbon black pellets.

BACKGROUND OF THE INVENTION

Carbon black is used today in large quantities as a rubber reinforcement agent. Large quantities of carbon black are sold in the form of pellets which are agglomerates of carbon black particles held together by rather small forces. These pellets when filled into bags, emptied from these bags, or generally during any frictional contact among themselves, develop carbon black dust which is undesirable.

THE INVENTION

It is thus one object of this invention to provide a carbon black pellet which is essentially dust free.

A further object of this invention is to provide a dust free carbon black pellet which when used as a rubber reinforcement agent does not introduce any materials foreign to the rubber formulation.

Yet a further object of this invention is to provide a process for producing dust free carbon black pellets.

Still another object of this invention is to provide an apparatus for carrying out a process for producing dust free carbon black pellets.

These and other objects, advantages, details, features and embodiments of this invention will become apparent to those skilled in the art from the following description of the invention, the appended claims and the drawing in which FIGS. 1 and 2 show schematical cross sections through an apparatus used in the production of the dust free carbon black pellets of this invention.

In accordance with this invention a dust free carbon black pellet is provided which consists essentially of a carbon black pellet core and a cover layer. The cover layer is a layer of rubber surrounding the carbon black pellet core. The rubber preferably is of the same general nature as the rubber into which the carbon black pellet is eventually blended for reinforcement purposes.

The rubber surrounding the carbon black pellet core can basically be any rubber. Preferably the rubber is composed essentially of conjugated alkadiene polymers or copolymers. More specifically, the rubber can be made predominantly out of copolymers of one or more conjugated alkadiene monomers of 4 to 8 carbon atoms and one or more vinyl arene monomers of 8 to 12 carbon atoms.

Any cross linking of the rubber during the process of producing the carbon black pellet can be prevented by either covering the carbon black pellet at a temperature well under the cross linking temperature or by incorporating a cross linking inhibitor into the rubber emulsion or solution or melt. Thus, the carbon black pellet of this invention may contain in the rubber layer a cross linking inhibiting quantity of such an agent. Examples of such cross linking inhibiting agents are: phthalic anhydride, benzoic acid, salicylic acid and the like known "retarding" agents.

The rubber that is preferably used as the cover layer is one of relatively low molecular weight and narrow molecular weight distribution. More specifically the molecular weight of the rubber surrounding the carbon black pellet core is in the range of about 10,000 to about 2,000,000 usually about 50,000 to 250,000 (weight average molecular weight) and the molecular weight distribution of such a rubber is preferably in the range of about 1.1 to about 5.5 which can be determined as described in U.S. Pat. No. 4,104,326.

A second embodiment of this invention resides in a process for producing a rubber covered carbon black pellet. This process consists in coating the carbon black pellet core with a layer of rubber as defined above. This covering step can either be done by contacting the carbon black pellet core with a solution of the rubber in a solvent to form a layer of said solution on the carbon black core and thereafter evaporating said solvent from the layer or it can also be done by covering the carbon black pellet with a layer of molten rubber at a temperature well above the softening point of the rubber and thereafter cooling the so-covered pellet to a temperature well below the softening temperature, or it can also be done using a rubber-aqueous emulsion, and thereafter evaporating the water.

Typical solvents that can be used in connection with the solution covering embodiment are benzene, toluene, and xylene.

In the process variation using the layer of molten rubber the covering temperature will usually be in the range of about 175° to about 300° C.

In accordance with another embodiment of this invention there is provided an apparatus for carrying out the process. This apparatus comprises a rotatably arranged cylindrical chamber with an inlet for carbon black pellet cores. The chamber is confined by a wall which at least in part is porous and connected to a source of rubber solution, emulsion, or melt under pressure. The chamber is also provided with withdrawal means for withdrawing the carbon black pellets covered with the rubber layer. Preferably the apparatus comprises an outer solid cylinder and a porous concentric inner cylinder. The inlet means for the carbon black pellets are arranged for discharging the carbon black pellets into the inner porous cylinder whereas the feed means for injecting the rubber solution or rubber emulsion, or molten rubber, are arranged for injecting these fluids into the annular space between the outer cylinder and the concentric inner porous cylinder.

FIG. 1 shows a longitudinal cross section through the apparatus for coating the carbon black pellets with a rubber layer. The apparatus comprises a coating chamber 1 which is composed of an external cylinder 2 and a concentric internal porous cylinder 3. The external cylinder 2 is closed at the two ends by front and end plates 4 and 5, respectively. Similarly the porous cylinder 3 is closed at the front end by a front plate 6 and at the downstream end by the same end plate 5 as the external cylinder. This arrangement establishes two zones, namely an inner zone 7 inside of the porous cylinder 3 and an annular zone 8 between the porous cylinder 3 and the external cylinder 2.

An inlet conduit 10 is provided for which is usually stationary. Two rotary seals 9 and 11 allow the fluid tight rotation of the cylinders 2 and 3 around this stationary feed conduit 10. Through feed conduit 10 carbon black pellets are introduced into the zone 7 within the porous cylinder 3.

A feed line 12 is provided for injection of the pellet covering material into the zone 8. This material can for instance, as illustrative of the invention, be a rubber emulsion 13. In the drawing the rubber emulsion 13 is shown to be present only in the lower portion of the annular zone 8 but it is within the contemplation of this apparatus to inject the latex solution under a significantly higher pressure such as to fill up the entire zone and increase the flow of the rubber emulsion through the pores 15 of the porous cylinder 3. The porous cylinder 3 is constructed out of material such as carbon steel. The coating cylinder system 1 is supported on a set of motor driven rolls 20. The end of the porous cylinder 3 is supported within the surrounding cylinder 2 by brackets 21.

During the rotation of the cylinder system 1 carbon black pellets 25 introduced via line 10 into space 7 tumble and roll in contact with the porous inner surface of cylinder 3 and thereby get in contact with the rubber emulsion whereby these pellets are covered with rubber emulsion. At the downstream end of the cylinder perforated buckets 26 lift the coated carbon black pellets and discharge them into a stationary chute 27. A rotary seal 28 provides for a fluid tight rotation of the downstream end plate 5 and the stationary chute 27.

The rubber emulsion coated carbon black pellets from chute 27 are discharged into a flash tank (not shown) in order to evaporate any water from the surface of these pellets. Preferably the pellets are introduced into the chamber 7 at a reasonably high temperature to effect evaporation of the water after having been coated with the rubber emulsion during the travel of the pellets along the length of the porous cylinder 3. The evaporated water leaving with the pellets through chute 27 can be recovered, after separation from the pellets and reused in the formation of the rubber emulsion.

The rubber covered carbon black pellets are primarily useful as reinforcement agents in rubber compositions used for the production of tires, hoses, and the like. In such a production these rubber covered pellets are broken apart in the mixing step thus releasing the carbon black into intimate admixture with the main batch of rubber.

The buckets 26 preferably are pervious, e.g., made out of a fine mesh material so that excess rubber emulsion can drain and be removed from the bucket. The area where the bucket is in contact with the porous cylinder 3 is, however, impervious to avoid any additional flow of rubber emulsion onto the already formed covered carbon black pellets. This is indicated in the drawing by the solid support 29 of the buckets 26.

In the flash dryer or liquid evaporator the temperature is adjusted to essentially prevent any fusing of the rubber covered carbon black pellets.

The following example is intended to describe calculated data without undue limitation of the scope of this invention.

EXAMPLE

In this example ranges and specific examples for operating conditions and parameters for a carbon black pellet covering operation as shown in the drawings is given. The reference numerals in parentheses refer to the drawing.

    ______________________________________                                                          Specific                                                                               Ranges                                                ______________________________________                                         (10) Carbon Black Pellets: (Dried)                                             Pounds/hour,       3,000*    --                                                Size range, mm,    0.25 to 2.0                                                                              --                                                Wt. % water,       0.5*      --                                                Type of Black, ASTM,                                                                              N339      --                                                Temperature, °F.                                                                           300       ambient to 350                                    (12) Rubber Emulsion:                                                          Pounds/hour,       100        30 to 300                                        Rubber concentration, wt. %                                                                       5          1 to 10                                          rubber in emulsion                                                             Pressure, psig,    2         1 to 5                                            Temperature, °F.,                                                                          125       ambient to 200                                    Composition: Styrene-butadiene                                                 rubber of 5 wt. % in water                                                     with conventional emulsi-                                                      fier as liquid                                                                 (27) Rubber-Coated Pellets (after drying, not shown):                          Pounds/hour,       3005      --                                                Wt. % carbon black,                                                                               99.3      98.5 to 99.4                                      Wt. % rubber,      0.2       --                                                Wt. % water,       0.5       --                                                Weight ratio of rubber to carbon                                                                            0.0004:1-0.004:1                                  black in the product                                                           Quality,           Dustless                                                    (2) Rotatable Shell:                                                           Diameter, ft.,     6         --                                                Length, ft.,       10        --                                                RPM,               12        10 to 15                                          (3) Porous Liner:                                                              Diameter, ft.,     5.5       --                                                Length, ft.,       9.5       --                                                Individual pore diameter, mm,                                                                     <0.25     --                                                Total pore opening,                                                                               3500      2000 to 6000                                      square inches,                                                                 Pore area/sq. ft., in.sup.2 /ft.sup.2                                                             21        about 12 to                                                                    about 36                                          (25) Depth of Pellets, Inches,                                                                    10        6 to 15                                           at rest:                                                                       Pressure within liner 3, psig,                                                                    -0.5       0 to -1                                          Pressure in annulus (8), psig,                                                                    3         1 to 10                                           ______________________________________                                    

Reasonable variations and modifications which will become apparent to those skilled in the art can be made in this invention without departing from the spirit and scope thereof. 

I claim:
 1. An apparatus for covering carbon black pellet cores with rubber comprising(a) a chamber confined by walls which at least in part are porous, (b) inlet conduit means for introducing carbon black pellet cores into said chamber, (c) latex conveyor means for causing the flow of rubber covering material from outside of the chamber through the porous walls and into the chamber, (d) means for causing relative motion between said chamber and the carbon black pellet cores therein, and (e) outlet conduit means for removing the rubber covered carbon black pellets.
 2. An apparatus in accordance with claim 1 wherein(a) said chamber is cylindrical, the cylindrical wall being porous, (b) the cylindrical chamber is arranged in a concentric cylindrical shell establishing an annular space between said shell and said porous cylindrical wall of said chamber, (c) said latex conveyor means comprise a conduit for introducing a rubber material into said annular and space, (d) said means for causing relative motion consist in a motor drive unit allowing to rotate the shell and chamber around their cylinder axis.
 3. An apparatus for covering carbon black pellet cores with rubber to produce rubber covered carbon black pellets comprising(a) a generally cylindrical chamber confined by walls comprising a generally cylindrical wall which walls at least in part are porous, (b) inlet conduit means for introducing carbon black pellet cores into said generally cylindrical chamber, (c) latex conveyor means for causing the flow of rubber covering material from outside of the generally cylindrical chamber through the porous walls and into the chamber, (d) means for causing relative motion between said generally cylindrical chamber and the carbon black pellet cores therein, and (e) outlet conduit means communicating with the interior of said generally cylindrical chamber for removing the rubber covered carbon black pellets from said generally cylindrical chamber.
 4. An apparatus in accordance with claim 3 wherein(a) at least a portion of said generally cylindrical wall is porous, (b) the generally cylindrical chamber is disposed within a concentric generally cylindrical shell establishing an annular space between said generally cylindrical shell and said porous generally cylindrical wall of said generally cylindrical chamber, (c) said latex conveyor means comprises a conduit communicating with said annular space for introducing a rubber material into said annular space, and (d) said means for causing relative motion comprises motor drive means drivingly engaging said generally cylindrical chamber for rotating said generally cylindrical chamber about its cylinder axis.
 5. An apparatus in accordance with claim 4 wherein said motor drive means is characterized as further drivingly engaging said generally cylindrical shell for simultaneously rotating said generally cylindrical shell and said generally cylindrical chamber about their common cylinder axis.
 6. An apparatus in accordance with claim 5 whereinsaid means for causing relative motion comprises drive means drivingly engaging said generally cylindrical chamber for rotating said generally cylindrical chamber above its cylinder axis, said outlet conduit means comprises an upwardly opening conduit inlet within said generally cylindrical chamber, and said generally cylindrical chamber carries bucket means therein for lifting rubber covered carbon black pellets from within said generally cylindrical chamber and discharging said thus lifted rubber covered carbon black pellets into said upwardly opening conduit inlet of said outlet conduit means in response to said rotating of said generally cylindrical chamber by said drive means.
 7. An apparatus in accordance with claim 6 wherein said bucket means comprises at least one bucket pervious to said rubber covering material and supported on the inner surface of said generally cylindrical wall of said generally cylindrical chamber whereby excess rubber covering material can drain from said at least one bucket as said rubber covered carbon black pellets are lifted from said rubber covering material in said generally cylindrical chamber in response to rotating of said generally cylindrical chamber by said drive means.
 8. An apparatus in accordance with claim 3 whereinsaid means for causing relative motion comprises drive means drivingly engaging said generally cylindrical chamber for rotating said generally cylindrical chamber about its cylinder axis, said outlet conduit means comprises an upwardly opening conduit inlet within said generally cylindrical chamber, and said generally cylindrical chamber carries bucket means therein for lifting rubber covered carbon black pellets from within said generally cylindrical chamber and discharging said thus lifted rubber covered carbon black pellets into said upwardly opening conduit inlet of said outlet conduit means in response to said rotating of said generally cylindrical chamber by said drive means.
 9. An apparatus in accordance with claim 8 wherein said bucket means comprises at least one bucket pervious to said rubber covering material and supported on the inner surface of said generally cylindrical wall of said generally cylindrical chamber whereby excess rubber covering material can drain from said at least one bucket as said rubber covered carbon black pellets are lifted from said rubber covering material in said generally cylindrical chamber in response to rotating of said generally cylindrical chamber by said drive means. 